SURPRISE, Ariz. — One morning this spring, Cam Gallagher paused for a moment and squatted into a crouch on the carpet near his locker, extending his glove low and outward. The impromptu demonstration caught the eye of teammate Ryan O’Hearn, who peered over in amusement from a few feet away. Yet for Gallagher, a 26-year-old Royals catcher, this was the easiest way to explain his secret skill.

“If a pitcher is going to mostly be down in the zone and we’re going to get those strikes,” Gallagher said, “we have to master these.”

One beat later, Gallagher held his crouch, mimicking his movements behind the plate. He pushed his glove forward, pretending to receive a low pitch out front.

“There’s not one way to do it,” he said.

Gallagher was here, demonstrating the value of receiving and pitch-framing because both advanced metrics and the Royals’ staff have rated him exceptional at the craft. In the minors, he graded out well above...